Vaccines have been utilized to provide a long term protection against a number of disease conditions by very limited administration of a prophylactic agent that stimulates an organism's immune system to destroy disease pathogens before they can proliferate and cause a pathological effect. Various approaches to vaccines and vaccinations are described in Bernard R. Glick and Jack J. Pasternak, Molecular Biotechnology, Principles and Applications of Recombinant DNA, Second Edition, ASM Press pp. 253–276 (1998).
Vaccination is a means of inducing the body's own immune system to seek out and destroy an infecting agent before it causes a pathological response. Typically, vaccines are either live, but attenuated, infectious agents (virus or bacteria) or a killed form of the agent. A vaccine consisting of a live bacteria or virus must be non-pathogenic. Typically, a bacterial or viral culture is attenuated (weakened) by physical or chemical treatment. Although the agent is nonvirulent, it can still elicit an immune response in a subject treated with the vaccine.
An immune response is elicited by antigens, either specific macromolecules, or an infectious agent. These antigens are generally either proteins, polysaccharides, lipids, or glycolipids, which are recognized as “foreign” by lymphocytes known as B cells and T cells. Exposure of both types of lymphocytes to an antigen elicits a rapid cell division and differentiation response, resulting in the formation of clones of the exposed lymphocytes. B cells produce plasma cells, which in turn, produce proteins called antibodies (Ab), which selectively bind to the antigens present on the infectious agent, thus neutralizing or inactivating the pathogen (humoral immunity). In some cases, B cell response requires the assistance of CD4 helper T cells.
The specialized T cell clone that forms in response to the antigen exposure is a cytotoxic T lymphocyte (CTL), which is capable of binding to and eliminating pathogens and tissues that present the antigen (cell-mediated or cellular immunity). In some cases, an antigen presenting cell (APC) such as a dendritic cell, will envelop a pathogen or other foreign cell by endocytosis. The APC then processes the antigens from the cells, and presents these antigens in the form of a histocompatibility molecule:peptide complex to the T cell receptor (TCR) on CTLs, thus stimulating an immune response.
Humoral immunity characterized by the formation of specific antibodies is generally most effective against acute bacterial infections and repeat infections from viruses, whereas cell-mediated immunity is most effective against viral infection, chronic intracellular bacterial infection, and fungal infection. Cellular immunity is also known to protect against cancers and is responsible for rejection of organ transplants.
Antibodies to antigens from prior infections remain detectable in the blood for very long periods of time, thus affording a means of determining prior exposure to a pathogen. Upon re-exposure to the same pathogen, the immune system effectively prevents reinfection by eliminating the pathogenic agent before it can proliferate and produce a pathogenic response.
The same immune response that would be elicited by a pathogen can also sometimes be produced by a non-pathogenic agent that presents the same antigen as the pathogen. In this manner, the subject can be protected against subsequent exposure to the pathogen without having previously fought off an infection.
Not all infectious agents can be readily cultured and inactivated, as is required for vaccine formation, however. Modern recombinant DNA techniques have allowed the engineering of new vaccines to seek to overcome this limitation. Infectious agents can be created that lack the pathogenic genes, thus allowing a live, nonvirulent form of the organism to be used as a vaccine. It is also possible to engineer a relatively nonpathogenic organism such as E. coli to present the cell surface antigens of a pathogenic carrier. The immune system of a subject treated with such a transformed carrier is “tricked” into forming antibodies to the pathogen. The antigenic proteins of a pathogenic agent can be engineered and expressed in a nonpathogenic species and the antigenic proteins can be isolated and purified to produce a “subunit vaccine.” Subunit vaccines have the advantage of being stable, safe, and chemically well defined; however, their production can be cost prohibitive.
A new approach to vaccines has emerged in recent years, broadly termed genetic immunization. In this approach, a gene encoding an antigen of a pathogenic agent is operably inserted into cells in the subject to be immunized. The treated cells are transformed and produce the antigenic proteins of the pathogen. These in vivo-produced antigens then trigger the desired immune response in the host. The genetic material utilized in such genetic vaccines can be either a DNA or RNA construct. Often the polynucleotide encoding the antigen is introduced in combination with other promoter polynucleotide sequences to enhance insertion, replication, or expression of the gene.
DNA vaccines encoding antigen genes can be introduced into the host cells of the subject by a variety of expression systems. These expression systems include prokaryotic, mammalian, and yeast expression systems. For example, one approach is to utilize a viral vector, such as vaccinia virus incorporating the new genetic material, to innoculate the host cells. Alternatively, the genetic material can be incorporated in a vector or can be delivered directly to the host cells as a “naked” polynucleotide, i.e. simply as purified DNA. In addition, the DNA can be stably transfected into attenuated bacteria such as Salmonella typhimurium. When a patient is orally vaccinated with the transformed Salmonella, the bacteria are transported to Peyer's patches in the gut (i.e., secondary lymphoid tissues), which then stimulate an immune response.
DNA vaccines provide an opportunity to immunize against disease states that are not caused by traditional pathogens, such as genetic diseases and cancer. Typically, in a genetic cancer vaccine, antigens to a specific type of tumor cell must be isolated and then introduced into the vaccine. An effective general vaccine against a number of cancers can thus entail development of numerous individual vaccines for each type of cancer cell to be immunized against.
One general approach to treatment of tumors involves administering angiogenesis inhibiting compounds to patients with growing tumors. Angiogenesis is the process by which new capillaries and blood vessels form. Angiogenesis is important in embryonic development, tissue growth, tissue repair, and tissue regeneration. In addition to these normal and essential processes, angiogenesis is also involved in many abnormal pathological processes such as tumor growth, tumor metastasis, and ocular vascular diseases such as diabetic retinopathy.
Angiogenesis involves a number of interdependent processes, including (a) activation of vascular endothelial cells, (b) decomposition of cell matrix proteins by endothelial cells expressing protease activity, (c) migration of endothelial cells to a potential growth sites, (d) proliferation of endothelial cells and (e) tube formation by differentiation of endothelial cells. Each of these processes is affected by a variety of promoter substances such as fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), and vascular endothelial growth factors (VEGF). The vascular endothelial growth factors (collectively VEGF) play a crucial role in endothelial cell growth and differentiation. VEGF acts by binding to receptor protein-tyrosine kinases present in the endothelial cell membranes, which in turn initiate a cascade of signal transduction reactions that stimulate cell growth.
Inhibition of pathological angiogenesis has been proposed as a treatment for tumors. See, for example, Folkman et al. Science, 221, 719, (1983). The basic concept of such treatment is that, since tumors require vascularization to grow, inhibition of blood vessel formation, through the administration of angiogenesis inhibiting compounds, will prevent tumor growth by starving the tumor of its blood supply. A disadvantage of his approach is that angiogenesis inhibitors must be administered on a relatively continuous basis to prevent tumor growth. A cessation in delivery of the inhibitor can lead to a resumption of tumor growth. A vaccine effective at inhibiting angiogenesis would be an attractive preventative agent against tumor formation.
There is a continuing need for a generally effective vaccine for immunization against angiogenesis, which can also inhibit the growth of a variety of tumors without the need for targeting specific tumor antigens. The present invention satisfies this need.